Wire mesh rivet

ABSTRACT

A wire mesh rivet ( 13 ) is provided which is used to produce a wire mesh isolator ( 11 ) in a bore ( 9 ) of a substrate such as a heat shield ( 7 ) for a vehicle exhaust system. The rivet ( 13 ) comprises a unitary wire mesh structure ( 19 ) which has a collar ( 15 ) and a shank ( 17 ). The collar ( 15 ) has a higher density than the shank ( 17 ), e.g., the collar ( 15 ) has the density of the finished isolator ( 11 ). The rivet ( 13 ) is formed into the finished isolator ( 11 ) by compressing the shank ( 17 ) to form a second collar, while restraining the original collar ( 15 ) from substantially changing its shape. The rivet ( 13 ) can include a metal insert ( 23 ) which prevents the wire mesh of the finished isolator ( 11 ) from experiencing high levels of compression when the substrate is fastened to its supporting structure. The rivets ( 13 ) can be carried by a dispensing strip ( 31 ) and can be formed into the finished isolator ( 11 ) using forming equipment ( 39 ) whose dimensions are compatible with the limited space available with some substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC §119(e) of U.S.Provisional Application No. 61/118,506 filed on Nov. 28, 2008, thecontents of which in its entirety is hereby incorporated by reference.

FIELD

This invention relates to wire mesh isolators for use in providingthermal and/or acoustical isolation for, among other things, the heatshields employed in vehicle exhaust systems.

BACKGROUND

Commonly-assigned U.S. Patent Publication No. 2006/0219860, the contentsof which are incorporated herein by reference, discloses unitary wiremesh isolators which are formed by inserting a wire mesh sleeve througha bore in a substrate, e.g., through a bore in a heat shield for avehicle exhaust system, and then compressing the portions of the sleevethat extend on either side of the substrate into collars larger than thebore so as to trap the wire mesh in place at the bore and form thedesired isolator. As detailed in the '860 application, the resultingunitary isolator solves a variety of problems associated withmulti-piece isolators, including difficulties arising from assemblingmultiple components in a manufacturing setting and the problem ofseparation of the isolator's components during shipping of assembledheat shields to vehicle manufacturers and/or during use of the heatshields.

Because the collars on both sides of the substrate arc formedsimultaneously in the '860 application, similar forming equipment isneeded on each side of the substrate. For many applications, the use ofsuch equipment is entirely acceptable. However, for some applications,only a limited amount of space is available on one side of thesubstrate. In particular, heat shields often have a concave and a convexside, with the concave side having a limited volume, especially in theregion of the bores where the isolators are located.

FIG. 1 shows representative examples of heat shields 7 for vehicleapplications, where the bores through the heat shields are shown by thereference number 9. In this figure. isolators 11 have been installed insome of the bores. As is evident from FIG. 1, the volume available forinstalling an isolator is limited for various of the bore locations.This is especially so for the undersides (concave sides) of boreslocated near the top of raised sections of a shield. Forming a wire meshcollar in such a limited volume using equipment of the type disclosed inthe '860 application can be challenging.

The present invention, in accordance with certain of its aspects,addresses this problem of forming a wire mesh isolator under conditionswhere the space available for producing the isolator's collar islimited. Both in connection with these aspects and with other aspects,the invention's methods and apparatus seek to simplify the installationof isolators in substrates, as well as to reduce the costs associatedtherewith.

SUMMARY

In accordance with a first aspect, the invention provides a rivet (13)comprising a unitary wire mesh structure (19) which has a central bore(21) and comprises a collar (15) and a shank (17), wherein the averagedensity of the collar (15) is greater than the average density of theshank (17), e.g., the average density is approximately 20% for thecollar (15) and approximately 10% for the shank (17).

In accordance with a second aspect, the invention provides a rivet (13)comprising:

(a) a unitary wire mesh structure (19) which has a central bore (21) andcomprises a collar (15) and a shank (17); and

(b) a metal insert (23) at least a part of which is within the centralbore (21);

-   wherein the metal insert (23) comprises a wall which has an exterior    surface and the exterior surface comprises at least two apertures    (27) for engaging the wire mesh of the central bore (21) of the    unitary wire mesh structure (19).

In accordance with a third aspect, the invention provides a rivetdispenser comprising a flexible strip (31) having a plurality ofapertures (33) and at least one wire mesh rivet (13) in one of theapertures (33), said wire mesh rivet (13) comprising a collar (15) and ashank (17), said apertures (33) being sized to retain the shank (17) andto allow the collar (15) to be pushed through the aperture (33), eachaperture (33) comprising a plurality of circumferemial flexible fingers(35) formed by slits (37) in the flexible strip (31), wherein:

(a) the number of flexible fingers (35) per aperture (33) is between 3and 16; and

(b) the length-to-width ratio of each flexible finger (35) is in therange of 1:1 to 3:1, e.g.. 1.6:1.

In accordance with a fourth aspect, the invention provides apparatus forforming a wire mesh isolator (11) comprising:

(a) a sleeve (55) which forms a cavity in which wire mesh is compressed,said sleeve (55) having a substrate engaging position; and

(b) a sensor (57) for determining when the sleeve (55) is in thesubstrate engaging position;

-   wherein:

(i) the apparatus prevents compression of the wire mesh prior to thesensor (57) signalling that the sleeve (55) is in its substrate engagingposition; and

(ii) the force applied to the substrate (7,65) by the sleeve (55) whenthe sleeve (55) is in its substrate engaging position is less than 10pounds.

In accordance with a fifth aspect, the invention provides apparatuscomprising a sleeve (47) and a wire mesh rivet (13) said wire mesh rivet(13) comprising a collar (15) whose outside diameter is OD_(collar),said sleeve (47) comprising a recess (49) for receiving the collar (15),said sleeve (47) having an outer surface whose maximum diameter at thelocation of the recess is OD_(sleeve), wherein OD_(collar) andOD_(sleeve) satisfy the relationship:

OD _(sleeve) /OD _(collar)≦1.1.

In accordance with a sixth aspect, the invention provides a method formaking a wire mesh rivet (13) having a collar (15) and a shank (17),said method comprising:

(a) providing a wire mesh tube (73) having a central bore;

(b) supporting the tube (73) by:

-   -   (i) inserting a first portion of the tube (73) into a first        cavity (81), said first cavity (81) having a fixed bottom (77)        and a moveable wall, e.g. a spring-loaded wall (79) ; and    -   (ii) inserting an arbor (71) into the tube's bore;

(c) surrounding a second portion of the tube (73) with a second cavity(83);

(d) reducing the volume of the second cavity (83) to form the rivet'scollar (15) by compressing the second portion of the tube (73) while notsubstantially reducing the volume of the first cavity (81); and

(e) reducing the volume of the first cavity (81) through movement of themoveable wall (79) relative to the fixed bottom (77) to form the rivet'sshank (17) by compressing the first portion of the tube (73);

-   wherein the second portion of the tube (73) is compressed to a    greater extent than the first portion of the tube (73) so that the    density of the collar (15) is greater than the density of the shank    (17).

The reference numbers used in the above summaries of the various aspectsof the invention are only fbr the convenience of the reader and are notintended to and should not be interpreted as limiting the scope of theinvention. More generally, it is to be understood that both theforegoing general description and the following detailed description aremerely exemplary of the invention and are intended to provide anoverview or framework for understanding the nature and character of theinvention.

Additional features and advantages of the invention are set forth in thedetailed description which follows and, in part, will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein. The accompanyingdrawings are included to provide a further understanding of theinvention, and are incorporated in and constitute a part of thisspecification. It is to be understood that the various features of theinvention disclosed in this specification and in the drawings can beused in any and all combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of representative heat shields with whichwire mesh isolators are used.

FIG. 2 is a perspective, cross-sectional view of a wire mesh rivetconstructed in accordance with certain aspects of the invention.

FIG. 3 is a cross-sectional view of a wire mesh rivet wherein the rivetincludes a metal insert in the form of a grommet and the grommetincludes barbs which engage the rivet's wire mesh structure.

FIG. 4 is a cross-sectional view of a wire mesh rivet wherein the rivetincludes a metal insert in the form of a grommet and the grommetincludes apertures which engage the rivet's wire mesh structure. Asshown in this figure, the apertures extend through the entire thicknessof the wall of the insert.

FIG. 5 is a cross-sectional view of a wire mesh rivet wherein the rivetincludes a metal insert in the form of a sleeve and the sleeve includesapertures which engage the rivet's wire mesh structure. As shown in thisfigure, the apertures extend through the entire thickness of the wall ofthe insert.

FIG. 6 is a cross-sectional view of a wire mesh rivet wherein the rivetincludes a metal insert that includes apertures which extend through theentire thickness of the wall of the insert. The figure illustrates theengagement of wire mesh with an aperture.

FIGS. 7A and 7B are cross-sectional and top view views, respectively, ofa metal insert in the form of a grommet which includes apertures whichextend partially through the thickness of the wall of the insert.

FIG. 8 is a perspective view of a dispensing strip carrying wire meshrivets.

FIG. 9 is a top view of the dispensing strip of FIG. 8 showing theflexible fingers used to engage the shanks of the mesh rivets.

FIG. 10 is a perspective view illustrating equipment for forming a wiremesh isolator from a wire mesh rivet at a bore of heat shield.

FIG. 11 is a perspective view of a portion of the isolator formingequipment of FIG. 10 with various parts removed to highlight features ofthe equipment's lower positioning assembly.

FIG. 12 is a side view, partially in section, of a portion of the lowerpositioning assembly of the isolator forming equipment of FIG. 10.

FIG. 13 is a cross-sectional view of a portion of the upper formingassembly of the isolator forming equipment of FIG. 10.

FIG. 14 is a side view illustrating the use of a dispensing strip toprovide wire mesh rivets to the isolator forming equipment of FIG. 10.Various parts have been removed for clarity.

FIG. 15 is a perspective view showing the formation of multipleisolators in a heat shield without the need to reposition the part.

FIGS. 16A and 16B are perspective cross-sectional views of examples ofwire mesh isolators produced from wire mesh rivets.

FIG. 17 is a cross-sectional view showing a tool for forming a wire meshtube into a wire mesh rivet. The tool is in its open position in thisfigure.

FIG. 18A is a cross-sectional view showing the tool of FIG. 17 in itsinitial closed position. FIG. 18B is a cross-sectional view showing theconfiguration of the wire mesh tube at this point in the process.

FIG. 19A is a cross-sectional view showing the configuration of the toolof FIG. 17 at the point where the rivet's collar has been formed. FIG.19B is a cross-sectional view showing the configuration of the wire meshtube at this point in the process.

FIG. 20A is a cross-sectional view showing the configuration of the toolof FIG. 17 at the point where both the rivet's collar and its shank havebeen formed. FIG. 20B is a cross-sectional view showing theconfiguration of the wire mesh tube at this point in the process, i.e,,it shows the completed wire mesh rivet.

The reference numbers used in the drawings refer to the following:

7 heat shield

9 bore in substrate (e.g., heat shield)

11 assembled wire mesh isolator

13 wire mesh rivet

15 collar of wire mesh rivet

17 shank of wire mesh rivet

19 unitary wire mesh structure of wire mesh rivet

21 bore of unitary wire mesh structure

23 metal insert

24 metal insert collar

25 barb on metal insert

27 a aperture which extends through entire thickness of wall of metalinsert

27 b aperture which extends partially through thickness of wall of metalinsert

29 wire mesh in aperture of wall of metal insert

31 dispensing strip

33 apertures in dispensing strip

35 flexible fingers of dispensing strip

37 slits of dispensing strip

38 feed notches of dispensing strip

39 isolator forming equipment

″forming assembly of isolator forming equipment

43 positioning assembly of isolator forming equipment

45 mandrel of positioning assembly

47 sleeve of positioning assembly

49 recess of sleeve of positioning assembly

51 mandrel of forming assembly

53 tamp of forming assembly

55 sleeve of forming assembly

56 cavity formed by inner wall of sleeve of forming assembly

57 sensor of forming assembly

59 wires for sensor

61 supporting structure for isolator forming equipment

63 second collar of wire mesh isolator

65 substrate

67 fastener

69 exhaust system component

70 rivet forming tool

71 arbor of rivet forming tool

73 rolled mesh tube

75 upper forming sleeve of rivet forming tool

77 stationary member of rivet forming tool

79 spring-loaded sleeve of rivet forming tool

81 first cavity of rivet forming tool

83 second cavity of rivet forming tool

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed above, in connection with certain of its aspects, theinvention provides wire mesh rivets for use in forming wire meshisolators. FIG. 2 shows a representative configuration for such a rivet.As shown in this figure, the rivet comprises a unitary wire meshstructure 19 which (a) has a bore 21 and (b) comprises a collar 15 and ashank 17. The unitary wire mesh structure is preferably formed from acontinuous piece of wire mesh, although multiple pieces can be united toform the unitary structure if desired.

As shown in, for example, FIGS. 3-7, mesh rivet 13 preferably includes ametal insert 23 which extends partially along central bore 21. Metalinsert 23 may be in the form of a grommet which has a collar whichengages the collar of the unitary wire mesh structure (see FIGS. 3, 4,6, and 7) or a simple sleeve without a collar (see FIG. 5). In eithercase, the primary function of the metal insert is to prevent the wiremesh from being excessively compressed when a heat shield is installedin a vehicle. As shown in FIG. 16, such installation involves theinsertion of a fastener 67 through the bore of the assembled isolatorand the tightening of the fastener to a component of the vehicle, e.g.,to a component of the vehicle's exhaust system. To ensure that the heatshield does not become loose during use, substantial torque is typicallyapplied to the fastener. Accordingly, the wall of the metal insert needsto have sufficient column strength to withstand the resultingcompressive forces.

Although the metal insert can simply be placed within the bore of theunitary mesh structure, preferably, the metal insert engages the meshstructure so as to minimize chances that the insert will separate fromthe mesh structure during shipment and handling of the rivet and/or theassembled isolator prior to final installation of the heat shield. FIG.3 shows the use of barbs 25 on the outside surface of the metal insertfor this purpose. Although the barb approach works satisfactorily, it isrelatively expensive since a substantial amount of metal (e.g., on theorder of 80%) needs to be removed from the part to form the barbs.

FIGS. 4-7 shows an alternate approach for retaining a metal insert inthe unitary mesh structure that is substantially less expensive in termsof material costs than the barb approach of FIG. 3. In accordance withthis approach, at least two apertures 27 are formed in the outer surfaceof the wall of the metal insert. During manufacture of the rivet (seebelow), wire mesh enters into the apertures (see, for example, referencenumber 29 in FIG. 6) and thus substantially locks the insert and thesleeve together.

The apertures can extend completely through the wall of the metal insertas shown by reference number 27 a in FIGS. 4-6 or only partially throughthe wall as shown by reference number 27 b in FIG. 7. The apertures thatextend completely through the wall can be produced by piercing the wall,while the apertures that extend partially through the wall can beproduced by broaching.

Broaching is generally less expensive than piercing. Also, because thebroached apertures only extend partially through the insert's wall, thewall retains more of its original column strength which, as discussedabove, is important in terms of withstanding the compressive forcesapplied to the insert during fastening of a heat shield to itssupporting structure. For both these reasons, apertures that extend onlypartially through the wall of the insert are generally preferred.

The average wire mesh density of the mesh rivet's collar is greater thanthe average wire mesh density of its shank. In particular, the averagedensity of the collar is substantially equal to the average density ofthe finished isolator, while the average density of the shank issubstantially less than the finished density. In this way, after beinginserted in the bore of a substrate (e.g., a bore in a heat shield), theshank can be compressed to form a second collar which has the density ofthe finished isolator (see below).

Quantitatively, the ratio of the average density of the rivet's shank tothe average density of the rivet's collar is in the range of 1:2 to 1:3,preferably in the range of 1:2 to 1:2.5, and most preferably,approximately 1:2. The density of the collar will depend on theparticular application, but generally, when expressed in percent, theaverage density of the rivet's collar is in the range of 15% to 25%.Accordingly, the density of the shank will generally be in the range of7.5% to 12.5%. Preferred collar and shank densities are approximately20% for the collar and approximately 10% for the shank.

As known in the art, the average density (D) in percent of a wire meshpart can be calculated by: (1) determining the weight (W) of the part,(2) determining the volume (V) of the part, (3) determining the density(p) of the wire making up the wire mesh, and (4) calculating the averagedensity from the equation: D=100*(W/(V*p)).

The difference in density between the rivet's collar and sleeve can beachieved using tooling of the type shown in FIGS. 17-20. FIG. 17 showstool 70 in its open condition with a rolled mesh tube 73 placed over anarbor 71 and, in this case, a barbed metal insert 23 placed on top ofthe mesh tube on the same arbor. FIG. 18A shows an upper forming sleeve75 coming down over arbor 71 and preparing to (a) drive the metal insert23 into the mesh tube and (b) form the collar 15 of the wire mesh rivet13. In this and subsequent steps, the mesh tube is supported on thebottom by stationary member 77. FIG. 18-B shows the shape of the wiremesh tube at this point in the process.

FIG. 19A shows the upper forming sleeve 75 forming and compressingcollar 15 from the upper portion of the mesh tube. What happens herethat needs to be understood is that as the upper forming sleeve iscoming down it bulges the mesh out just above spring-loaded sleeve 79.In particular, the shoulder at the top of spring-loaded sleeve 79prevents the mesh tube from traveling downward. The more the uppersleeve goes down the more the mesh encroaches over the spring-loadedsleeve further preventing the mesh tube and, in particular the meshshank, from traveling axially. As a result of this process, thedensities of both the collar and the shank are increased, with thedensity of the collar being increased much more than the density of theshank. FIG. 19A shows the resulting structure.

FIG. 20A shows the upper sleeve continuing even further downward, but inthis case it has overcome the springs (not shown) of spring-loadedsleeve 79. As a result, the shank portion of the tube is furthercompressed to its final density. FIG. 17D-2 shows the resulting finishedwire mesh rivet 13 with the rivet's collar 15 having a higher densitythan its shank 17.

It should be noted that when a metal insert having an aperture 27 awhich extends completely through the insert's wall is used, arbor 21prevents the mesh from flowing into the bore of the rivet as collar 15is formed. That is, the wire mesh enters the aperture, but is stoppedfrom entering the rivet's bore by the arbor. Wire mesh also entersapertures 27 b as the collar is ibrmed in cases where apertures whichextend only partially through the thickness of the wall of the metalinsert are used.

The wire mesh making up the wire mesh structure can be composed ofvarious materials and those materials can be subjected to varioustreatments (including coatings) either before or after being formed intoa mesh. Examples of suitable materials and treatments include, withoutlimitation, carbon steel, stainless steel, 300 and 400 series,tin-plated carbon steel, zinc-plated carbon steel, and galvanized carbonsteel. The wires making up the wire mesh can have variouscross-sections, including, without limitation, round, hexagon, octagon,square, and flat. The wire mesh is preferably a knitted wire mesh,although other types of wire meshes, e.g., woven and expanded metalmeshes, can be used if desired.

The wire mesh rivets are preferably mounted in a dispensing strip priorto being provided to users, e.g., heat shield manufacturers. FIGS. 8 and9 show a suitable configuration for such a dispensing strip. As can beseen in these figures, dispensing strip 31 includes a plurality ofapertures 33 sized to received the shanks 17 of rivets 13 and to allowcollars 15 to be pushed through the apertures. Apertures 33 comprise aplurality of flexible fingers 35 formed by slits 37 in the body of thestrip. As can be seen in FIG. 9, dispensing strip 31 can include notches38 for use in feeding the strip to isolator forming equipment, e.g.,equipment 39 of FIGS. 10 and 11 discussed below.

As discussed below, the dispensing strip facilitates automation of theprocess which converts wire mesh rivets into wire mesh isolators. Assuch, the dispensing strip needs to satisfy a number of competingcriteria. First, the strip needs to hold the rivets sufficientlysecurely so that the rivets do not become misaligned or dislodged fromthe strip during transport and handling. Typically, the strip will becoiled in a shipping container and dispensed directly from thecontainer. Accordingly, the strip is preferably flexible enough to bewrapped into a coil while still minimizing misalignment and dislodgementof the rivets when coiled. Second, the rivets must be readilydispensable from the strip. In particular, the strap must havesufficient strength so that it does not buckle under the forces appliedto the rivet during dispensing. Such buckling is undesirable since itcan cause the strip to partially or completely lose engagement with thestrip's feed mechanism. Third, the strips must be inexpensive so thatthey can be a disposable item.

In practice, it has been found that the number and length-to-width ratioof flexible fingers 35 are important parameters in meeting thesecriteria for a strip composed of a low cost plastic material, such asplasticized styrene. Thus, less than 3 flexible fingers results inunacceptably high dispensing forces, as does a length-to-width ratio ofless than 1:1. On the other hand, more than 16 flexible fingers resultsin unacceptable levels of dislodgement of the rivets from the strip, asdoes a length-to-width ratio greater than 3:1.

Accordingly, the number of fingers 35 per aperture is preferably in therange of 3-16. As to the length-to-width ratio of the individualfingers, this parameter is preferably in the range of 1:1 to 3:1, e.g.,1.6:1. These ranges have been found to work successfully with wire meshrivets having dimensions suitable for use in producing wire meshisolators for vehicle heat shields, e.g., with wire mesh rivets havingshank and collar OD dimensions of approximately 14 millimeters and 22millimeters, respectively.

Turning now to the process for producing wire mesh isolators from thewire mesh rivets., in broad outline, a wire mesh rivet 13 is transformedinto a wire mesh isolator 11 by inserting the rivet's shank 17 in a borein a substrate 65 (e.g., a bore 9 in a heat shield) with collar 15engaging one side of the substrate (the proximal side of the substrate)and then compressing the portion of the shank which extends beyond thedistal side of the substrate into a second collar 63 (see FIG. 16).Preferably, the proximal and distal collars 15 and 63 of the finishedisolator 11 have substantially equal densities since unequal densitiescan cause the isolator to have compromised thermal and/or vibrationalproperties. The proximal and distal collars also will generally havesubstantially equal diameters and thicknesses, although they can beunequal if desired (see, for example, the collars of FIG. 16).

In U.S. Patent Publication No. 2006/0219860 referred to above, theproximal and distal collars are formed simultaneously which requiressimilar forming equipment on both sides of the substrate. For some heatshield configurations (see FIG. 1), locating the forming equipment onthe concave side of the heat shield is challenging because of thelimited space available. The use of wire mesh rivets having a preformedcollar eliminates this problem because compared to forming equipment,less bulky equipment is needed to locate the rivet in the bore and holdit in place while the collar on the opposite side of the substrate isbeing for med.

FIGS. 10 and 11 show representative isolator forming equipment 39 whichtakes advantage of this aspect of the invention. The equipment includesan upper forming assembly 41 and a lower positioning assembly 43. Itshould be noted that the reference to the “upper” forming assembly andthe “lower” positioning assembly are only for convenience ofdescription, it being understood that the positioning assembly and theforming assembly can be reversed or can be oriented at an angle otherthan vertical, e.g., horizontally, if desired.

FIG. 10 shows the equipment 39 in use while FIG. 11 shows the sameequipment with heat shield 7 removed as well as much of the upperforming assembly 41. The limited amount of equipment needed for thelower positioning assembly 43 is evident in FIG. 11.

FIG. 12 shows the lower positioning assembly 43 in more detail. As canbe seen in this figure. the assembly comprises two main parts—a mandrel45 which engages the bore 21 of the rivet's wire mesh structure 19 and asleeve 47 which includes a recess 49 which receives the rivet'spreformed collar 15 and maintains the collar's shape as the wire meshcollar on the opposite side of the substrate is formed. By minimizingthe difference between the outside diameter (OD) of sleeve 47 at thelevel of the recess and the outside diameter of preformed collar 15, thelower positioning assembly's footprint as seen from the substrate is notmuch larger than the footprint of the wire mesh rivet itself. Inpractice, the OD of sleeve 47 can be held to be within 10% of the OD ofthe rivet's collar, i.e., OD_(sleeve)/OD_(collar)≦1.1. Such a smallfootprint for the lower positioning assembly greatly facilitates theformation of wire mesh isolators for substrates having curved surfaces,such as various of the heat shields of FIG. 1.

FIG. 13 shows the upper forming assembly 41 in more detail. Thisassembly includes a mandrel 51 which engages the bore 21 of the rivet'swire mesh structure 19 and a tamp 53 which, during use of the assembly,moves downward to the position shown in FIG. 13 to compress the wiremesh of shank 17 within the confines of sleeve 55, i.e., within thecavity 56 formed by the inner wall of sleeve 55, to form the secondcollar of the isolator, i.e., the collar on the upper side of the heatshield in FIG. 10. During the formation of the second collar, mandrels45 and 51 of the lower positioning assembly and the upper formingassembly maintain an open bore along the entire length of the rivet and,as it is formed, the finished isolator. As discussed above, recess 49 insleeve 47 of positioning assembly 43 constrains collar 115 from changingits shape as forming assembly 41 forms the second collar. As a result ofthese constraints applied by the mandrels and this recess, finished wiremesh isolators are produced which have well defined OD and ID dimensionsand collars with substantially equal wire mesh densities.

As shown in FIG. 13, forming assembly 41 preferably includes a sensor57, e.g., a proximity switch, for detecting the position of sleeve 55.The sensor is connected to a control system (not shown) by wires 59 (seeFIGS. 10 and 11). The control system allows mandrel 51 and tamp 53 tomove towards the substrate only if the sensor indicates that sleeve 55is in its most forward position, i.e., the control system only allowsthe mandrel and tamp to move forward if sleeve 55 is in engagement withthe surface of the substrate, thus preventing an operator's hands fromcoming into contact with the mandrel and tamp. Sleeve 55 is itselflightly sprung so that its motion does not present a hazard to personneloperating the forming equipment. In particular, the force applied by thesleeve to the substrate is less than 10 pounds. In this way, the formingequipment avoids injury to operating personnel without the need for alight curtain or similar device to ensure that the equipment is notoperated while the operator's hands are close to the equipment. Ifdesired, more than one sensor for the position of sleeve 55 can beemployed to provide redundant protection.

Although not shown in FIGS. 10 and 11, a dispensing strip 31 ispreferably employed to supply wire mesh rivets to isolator formingequipment 39. FIG. 14 shows such an embodiment. In particular, thisfigure shows positioning assembly 43 after it has removed a mesh rivet13 from strip 31 and has moved it upward to enter the bore of asubstrate (not shown). Forming assembly 41 (not shown in this figure)would then compress the shank 17 of the rivet to form second collar 63of the finished isolator 11.

FIG. 15 shows an embodiment in which multiple isolators are formed atdifferent locations of a single substrate (e.g., a single heat shield)without the need to reposition the part. As can be seen in this figure,supporting structures 61 hold a plurality of upper forming assemblies 41and lower positioning assemblies 43 in place relative to heat shield 7so that isolators can be formed at each of the shield's bores.Preferably, the isolators are formed simultaneously, although sequentialformation (e.g., singly or in groups) can be employed if desired.Although not shown in this figure, dispensing strips 31 are preferablyused to provide wire mesh rivets to each of the lower positioningassemblies.

A variety of modifications that do not depart from the scope and spiritof the invention will be evident to persons of ordinary skill in the artfrom the foregoing disclosure. For example, although the invention hasbeen illustrated in terms of heat shields employed in vehicle exhaustsystems, it can be used in a variety of other applications where thermaland/or acoustical isolation is desired. Similarly, the invention is notlimited to the particular types of heat shields illustrated herein butcan be used with other heat shields now known or subsequently developed.Also, the invention can be used with single layer metal substrates ormore complex substrates having multiple metal layers or a combination ofmetal and non-metallic layers, e.g., layers of ceramic or glass fibers.The following claims are intended to cover these and othermodifications, variations, and equivalents of the embodiments disclosedherein.

1. A rivet comprising a unitary wire mesh structure which has a centralbore and comprises a collar and a shank, wherein the average density ofthe collar is greater than the average density of the shank.
 2. Therivet of claim 1 wherein the ratio of the average density of the shankto the average density of the collar is in the range of 1:2 to 1:3. 3.The rivet of claim 2 wherein the average density of the rivet's collaris in the range of 1:5% to 25%.
 4. A rivet comprising: (a) a unitarywire mesh structure which has a central bore and comprises a collar anda shank; and (b) a metal insert at least a part of which is within thecentral bore; wherein the metal insert comprises a wall which has anexterior surface and the exterior surface comprises at least twoapertures for engaging the wire mesh of the central bore of the unitarywire mesh structure.
 5. The rivet of claim 4 wherein the at least twoapertures are substantially completely filled with the wire mesh of theunitary wire mesh structure.
 6. The rivet of claim 4 wherein the atleast two apertures extend partially through the thickness of the wall.7. The rivet of claim 6 wherein the apertures are formed by broaching.8. The rivet of claim 4 wherein the at least two apertures extendcompletely through the thickness of the wall.
 9. The rivet of claim 8wherein the apertures are formed by piercing.
 10. A rivet dispensercomprising a flexible strip having a plurality of apertures and at leastone wire mesh rivet in one of the apertures, said wire mesh rivetcomprising a collar and a shank, said apertures being sized to retainthe shank and to allow the collar to be pushed through the aperture,each aperture comprising a plurality of circumferential flexible fingersformed by slits in the flexible strip, wherein: (a) the number offlexible lingers per aperture is between 3 and 16; and (b) thelength-to-width ratio of each flexible finger is in the range of 1:1 to3
 1. 11. The rivet dispenser of claim 10 comprising a wire mesh rivet ineach of the apertures.
 12. Apparatus for forming a wire mesh isolatorcomprising: (a) a sleeve which forms a cavity in which wire mesh iscompressed, said sleeve having a substrate engaging position; and (b) asensor for determining when the sleeve is in the substrate engagingposition; wherein: (i) the apparatus prevents compression of the wiremesh prior to the sensor signalling that the sleeve is in its substrateengaging position; and (ii) the force applied to the substrate by thesleeve when the sleeve is in its substrate engaging position is lessthan 10 pounds.
 13. Apparatus comprising a sleeve and a wire mesh rivetsaid wire mesh rivet comprising a collar whose outside diameter isOD_(collar), said sleeve comprising a recess for receiving the collar,said sleeve having an outer surface whose maximum diameter at thelocation of the recess is OD_(sleeve), wherein OD_(collar) andOD_(sleeve) satisfy the relationship:OD _(sleeve) /OD _(collar)≦1.1.
 14. A method for making a wire meshrivet having a collar and a shank, said method comprising: (a) providinga wire mesh tube having a central bore; (b) supporting the tube by: (i)inserting a first portion of the tube into a first cavity, said firstcavity having a fixed bottom and a moveable wall; and (ii) inserting anarbor into the tube's bore; (c) surrounding a second portion of the tubewith a second cavity; (d) reducing the volume of the second cavity toform the rivet's collar by compressing the second portion of the tube,while not substantially reducing the volume of the first cavity; and (e)reducing the volume of the first cavity through movement of the moveablewall relative to the fixed bottom to form the rivet's shank bycompressing the first portion of the tube; wherein the second portion ofthe tube is compressed to a greater extent than the first portion of thetube so that the density of the collar is greater than the density ofthe shank.
 15. The method of claim 14 wherein the moveable wall isspring-loaded.